1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a small structure such as a gyroscope, an accelerometer, a micro-mirror and so forth, and a method for fabricating the same, and more particularly to a small structure having a floating body and a method for fabricating the same.
2. Description of the Related Art
In general, a small structure using microelectromechanical technology, such as a gyroscope, an accelerometer and a micro-mirror is provided with a mass, such as a vibration piece, which constantly vibrates or rotates in a first axial direction. When such a mass rotates in a second axial direction perpendicular to the first axial direction at a constant angular velocity, the mass generates a coriolis force in a third axial direction, which is perpendicular to the first and second axial direction. According to this coriolis force, the mass generates a minute displacement, for example between tens of nanometers and several nanometers. This displacement is sensed by variation of capacitance, and detected as a rotational angular velocity.
However, this gyroscope is generally used under the exposure to a disturbance, such as noise, impact etc., other than the rotational angular velocity. When this type of disturbance acts on the gyroscope, the mass of the gyroscope generates displacement due to translational acceleration. As a result, a certain component of the displacement caused by the translational acceleration causes the mass to be displaced in the sensing direction, so that undesired signals are detected.
Therefore, the gyroscope is essentially required to isolate the mass from the disturbance such as noise, impact etc. introduced from an external environment.
Referring to FIG. 1, there is illustrated a general gyroscope 1, wherein an oscillator including an oscillating piece as a mass is isolated from a disturbance by means of an resilient member.
The gyroscope 1 is composed of a resilient member 4 enclosing an oscillator 2 and a printed circuit base (PCB) 3, and a housing 5 which receives the resilient member 4.
In this conventional gyroscope 1, the resilient member 4 is sealed in the housing 5 in a slightly compressed state so as not to move in the housing 5. Hence, when the resilient member 4, which encloses the oscillator 2 and the PCB 3, is sealed in the housing 5, a force applied to the oscillator 2 by the resilient member 4 is varied before and after sealing, so that the gyroscope is changed in output after sealing.
For this reason, in order to adjust the output after sealing, the gyroscope 1 should provide an output adjusting hole for the housing 5. As a result, the housing 5 fails to insulate a noise, etc.
In order to improve this problem, there has been proposed a gyroscope 1′ having a structure such that no force is applied to a resilient member when the resilient member is sealed in a housing, as shown in FIGS. 2 and 3. This technology is disclosed in Japanese Patent Application Publication No. 2002-213960.
The gyroscope 1′ is composed of an oscillator 12 having a base 18 supporting an oscillating piece 14 (FIG. 3) by means of a supporting pin 16, wherein the oscillating piece 14 includes electrodes bonded to an outer surface by a piezoelectric element; a PCB 24 fixing resilient lead frames 20 of the base 18 to electrode pads 24a by soldering and having chip type electronic elements mounted thereon; resilient members 22 receiving the base 18 to prevent noise, vibration etc. from being transmitted to the base 18; and a stem 26 having a plurality of input/output lead pins 28.
The PCB 24, the resilient members 22 and the stem 26 are integrally fixed by disposing the resilient members 22 between the PCB 24 and the stem 26 and by soldering first ends of the lead pins 28 to through holes 24b of the PCB 24.
An upper cover 30 is fixed on the stem 26 by welding so as to seal the PCB 24 and the resilient members 22.
This conventional gyroscope 1′ does not bring the upper cover 30 into contact with the resilient members 22, so that, when the upper cover 30 is fixed, the oscillator 12 protected by the resilient members 22 is not pressed and displaced. Thus, there is an advantage in that, after the upper cover 30 is fixed, the gyroscope does not generate a change in output. However, the resilient members 22 should be separately fabricated, and also separate processes of maintaining the resilient members 22 between the PCB 24 and the stem 26 and of soldering the first ends of the lead pins 28 to the through holes of the PCB 24 in order to install the resilient members 22 are required, so that there is a problem in that the gyroscope has difficulty of assembling and increase of production costs.
Further, in the conventional gyroscope 1′, the lead pins 28, which are fixed to the stem 26, are directly fixed to the PCB 24, so that when any disturbance takes place, the disturbance is directly transmitted to the PCB without being isolated. Thus, the oscillator 12 generates displacement by means of translational acceleration, thus causing undesired signals to be detected.